Abstract
BACKGROUND: Spontaneous pneumothorax should be classified as primary spontaneous pneumothorax (PSP) or secondary spontaneous pneumothorax (SSP) because treatment strategies may differ depending on underlying lung conditions and clinical course. The pulmonary dysfunction can lead to changes in end-tidal carbon dioxide (ETCO(2)). The aim of this study was to investigate the difference in ETCO(2) between PSP and SSP. METHODS: This retrospective observational study included adult patients diagnosed with spontaneous pneumothorax in the emergency room from April 2019 to September 2020. We divided patients into PSP and SSP groups and compared ETCO(2) variables between the two groups. RESULTS: There were 33 (66%) patients in the PSP group and 17 (34%) patients in the SSP group. Initial ETCO(2) was lower in the SSP group than in the PSP group (30 (23-33) vs. 35 (33-38) mmHg, p=0.002). Multivariate analysis revealed that respiratory gas associated with SSP was initial ETCO(2) (OR: 0.824; 95% CI: 0.697-0.974, p=0.023). The optimal cutoff for initial ETCO(2) to detection of SSP was 32 mmHg (area under curve, 0.754), with 76.5% sensitivity and 72.7% specificity. CONCLUSION: ETCO(2) monitoring is a reliable noninvasive indicator of differentiating between PSP and SSP. Initial ETCO(2) lower than 32 mmHg is a predictor of SSP.